The U.N. envoy for Yemen urged the warring parties Wednesday to maintain the momentum of the initial pullout of Houthi rebel forces from three ports by moving quickly to larger joint withdrawals — and to work urgently on a political solution to the devastating conflict.

Martin Griffiths told the Security Council there are "signs of hope" but also "alarming signs in recent days" that progress can be threatened.

He pointed to an escalation of violence in Yemen's southern Dhale province, which had been under the control of forces loyal to the internationally recognized government. He also expressed serious concern at news of a drone attack Tuesday on oil facilities in neighboring Saudi Arabia, saying that "we cannot ignore how these developments affect the political process."

The conflict in Yemen began with the 2014 takeover of the capital, Sanaa, by the Iran-backed Houthis. A Saudi-led coalition allied with Yemen's government has been fighting the Houthis since 2015.

The fighting in the Arab world's poorest country has killed thousands of civilians, left millions suffering from food and medical care shortages and pushed the country to the brink of famine.

"Yemen remains at the crossroads between war and peace," Griffiths said, despite the significance of the U.N.-monitored Houthi withdrawals from the key port of Hodeida and the smaller ports of Salif and Ras Issa between Saturday and Tuesday. The port at Hodeida handles about 70 percent of Yemen's commercial and humanitarian imports and its security is now in the hands of the coast guard.

Griffiths said the withdrawals must be followed by "concrete actions" by the government and the Houthis to deliver on their commitments to further redeployments under the agreement signed in Sweden in December.

But Yemeni Ambassador Abdullah Ali Fadhel Al-Saadi protested to the council at the Houthis' unverified "unilateral redeployment" outside the agreement. He called it an attempt "to prolong the war," saying the Houthis "are now puppets in the hands of mullahs and the Iranian regime."

Al-Saadi told the council the government reaffirms its right to verify what happens as a party to the December agreement "before beginning any discussions of any kind of upcoming phases."

Lt. Gen. Michael Lollesgaard, head of the U.N. mission overseeing the redeployment, said in a video briefing that after four months of "very difficult discussions" and no implementation of the December agreement, "we got a little impatient" and accepted the Houthi offer to "kick-start" progress.

Under the agreement, there is a two-phase withdrawal process — the first a pullback of several kilometers (miles) by the Houthis and coalition forces, and the second a withdrawal of 18 to 30 kilometers (11 to 18 1/2 miles), depending on the location and fighters, according to a U.N. official.

Lollesgaard said the Houthis insist there is no gap between the first and second phases.

Once the second phase is completed, he stressed that there will be a complete verification process — by the Yemeni government, the Houthis and the U.N.

Both sides have agreed on the operational plan for phase one and Griffiths urged them to agree on the plan for phase two.

Lollesgaard said key outstanding issues for phase two are deciding how far troops will withdraw from the center of Hodeida city, determining which side moves first, and reaching an agreement on local security forces that will take over security.

The U.N. now has just 15 monitors and he urged the Houthis to speed up issuing visas for 30 more.

Griffiths urged the Security Council to welcome the redeployments, urge the parties to work quickly to implement the remaining withdrawals, and work urgently with the U.N. on a political solution.

"These beginnings, these early shoots, must be protected from the threat of war," Griffiths said. "We must not allow war to take peace off the table."

U.N. humanitarian chief Mark Lowcock told the council that 10 million Yemenis are relying on food assistance to survive and "the specter of famine still looms."

A resurgent cholera outbreak has affected 300,000 people so far this year — compared to 370,000 during all of 2018, he said.

Henrietta Fore, head of the U.N. children's agency UNICEF, told the council that since the fighting began in Yemen four years ago, 7,300 children have been killed or injured, and the numbers are no doubt higher because these are verified numbers.

She said 360,000 children are suffering from severe acute malnutrition and half the children under the age of five — 2.5 million — are stunted, "and stunting is irreversible."

"Yemen is spiraling perilously close to the brink," Fore said.

Copyright 2018 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.